Vacuum apparatus



QIVENTOR.

ATTORNEY R'. DORWALD E L YACUUM APPARATUS Filed May 4, 1964 March 7,1967 2 2 Q Q g United States Patent 3,307,577 VACUUM APPARATUS RudolfDiirwald and Helmut Reisinger, both of Triesen, Liechtenstein,assignors, by mesne assignments, to Bendix Balzers Vacuum, Inc.,Rochester, N.Y., a corporation of Delaware Filed May 4, 1964, Ser. No.364,400

Claims priority, application Austria, May 21, 1963,

1 Claim. (Cl. 137-567) The present invention concerns a vacuum apparatuswith a receiver, for example an electronmicroscope or an electrondiffraction apparatus, to which is connected a pumping system consistingof a diffusion pump and a forevacuum pump, and which possesses a lockchamber for the introduction or removal of objects.

With such equipment it is frequently very disturbing if the forevacuumpump must be kept running during the operation; often the noise or themechanical vibration caused by the running pump or the stray magneticfield produced by the motor of the pump are disturbing while observingthe electronmicroscope picture; It is therefore proved to be generallyuseful to provide for a socalled forevacuum reservoir in such pumpsystems, that is a reservoir which helps to replace the forepump of thediffusion pump so long as a given maximum pressure is not exceeded init. This maximum pressure corresponds to the maximum permissablepressure on the exhaust side of the diffusion pump (forepressurebreakdown) at which it can still carry out its pump function directly;if this pressure is exceeded the pump action breaks down. The period,during which the forepump can remain cut off longest, thus the maximumtime at ones disposal for undisturbed work with an electronmicroscopevaries with, the size of the so-called forevacuum reservoir, theforepressure breakdown of the diffusion pump, the volume of thelockchamber, the gas evolution and the leak tightness of the reservoiras well as with the interval between each two introductions. Should thetime span for undisturbed work be required to be large, an unwieldlylarge vacuum reservoir would become necessary, especially so, if, aswith electronmicroscopes, electron diffraction apparatus and the like,new objects must be introduced into the apparatus through a lockchamber, where each time a'large amount of air also penetrates. Theobject of the invention is to eliminate thesedisadvantages.

According to the invention it is proposed that in a vacuum system with areceiver, a diffusion pump for exhausting the receiver, a forevacuumpump and lock chamber for introducing and removing objects from thereceiver, to provide a first and second vacuum reservoir for saidsystem. One vacuum reservoir into which the diffusion pump can exhaustand the other reservoir provided for the lock chamber.

Only limited space is available in vacuum equipment for the installationof forevacuum reservoirs. Utilization of the available space, accordingto the invention, for two seperate forevacuum reservoirs, permits one toachieve, in a surprising way, a significantly longer, undisturbed,operating time with the pump shut off. It is possible in this way toaccumulate in a given total volume for both forevacuum reservoirs abouta 50 fold or more greater amount of gas, before the forevacuum pump mustagain be operated, than is the case for only one fore vacuum reservoirof the same total volume.

An embodiment of the invention will be explained by an example and theaccompanying sketch.

In the sketch, 1 represents the receiver, 2 a diffusion pump connectedto the receiver through a valve 3 (in the case of the example) 4represents a vapor jet pump ice installed before the diffusion pump(this may be omitted if desired), and 5 a first forevacuum reservoir,which, as was mentioned, has the task of receiving the gases expelledfrom the diffusion or vapor jet pumps, while the forevacuum pump is shutoff. The insertion of a vapor jet pump gives the advantage, that themaximum permissible pressure in the reservoir 5 corresponds to thehigher forepressure breakdown of a vapor jet pump which is greater incomparison to that of a diffusion pump. The parts mentioned to thispoint are connected with each other through pipes 6, 7 and 8, as isevident from the sketch, while the forevacuum reservoir 5 is connectedwith the forevacuum pump 9 through the valve 10 and through these mustbe brought to a reduced pressure from time to time, which pressure willbe chosen to be so low 0.1 torr), that it can be taken as practicallyequal to zero for all subsequent considerations. In a known manner, aso-called bypass line, for the purpose of evacuating the receiver,bypasses the diffusion pump and connects the receiver 1 through a valve11 with the forepump 9 as well as a valve 12 for the inlet ofatmospheric air into the receiver (flooding).

A lock chamber 13 for the introduction and removal of objects is addedto the equipment. This is represented schematically in the sketch, sincethe design details of the lock as well as the holding and movingarrangements for the objects or preparations for the electronmicroscopeare not of interest for the description of the invention. Theconnections to the lock chamber are shown according to their function,on the one side with the receiver, on the other side with the atmospherefrom which the system is isolatable by the valves 14 and 15. In order tobring an object into receiver, it is placed in the chamber 13 throughthe valve 15 and after closing valve 15 and opening valve 14 theinsertion ofthe object into the receiver can be worked out in differentways by means of suitable known transport mechanisms. The removal occursin reverse order. Often the main point is to place the lock chamber incommunication with the receiver, whereby the object can remain in thechamber 13, for example, in preparations for the electronmicroscope. Inthe operation of the described equipment by procedures and methods knownup to now, the gas present in the lock chamber would be removed eitherafter opening the valve 14 through the pump 2 or through the bypassline. Equipments are also known, in which the lock chamber is providedwith its own evacuation line. So far the equipment described up to nowhas shown no novelty and corresponds to the known state of the art.

However, according to the invention a second separated forevacuumreservoir 16 is provided for the lock and is connected with it throughthe pipe 17, isolatable through the valve 18, and connected to thesuction side of the forevacuum pump through the pipe 19. For operationof the equipment the two forevacuum reservoirs 5 and 16 are firstbrought to a reduced pressure by the forepump which is necessary for theoperation of the diffusion or vapor jet pumps. Thereupon the valves 10,11 and 20 are closed. The pumps 2 and 4 can remain in operation and thereceiver further evacuated or held at a fixed pressure, until throughthe gas accumulation; (introduced through the outgassing of theassembled parts and inner walls and the objects brought in, or throughair, which is introduced through leaks or through the lock) the pressurein 5 is increased beyond the above mentioned maximum pressure. Then theforevacuum pump must again be put in operation.

The optimal distribution of the available volume for the two forevacuumreservoirs together can be easily determined according to the knownformulas of the theory of gases, since it depends, as has beenmentioned,

on the forepressure breakdown of the diffusion or vapor jet pumps putinto the system, on the gas accumulation from the recipient and from thelock chamber and on the volume of the lock chamber. Further, the numberof lockings per second, the interval between each two storage time spanin the first and second forevacuum reservoirs, measured in torr litersand P (V +V states the amount of gas that can be stored, if V and Vtogether form only a single forevacuum reservoir. The factor is ameasure of the technical step forward pro- 5 lockings as well as thenecessary duration of undisturbed duced by the lnventlon. readiness foroperation must be taken into consideration The following table gives thedata for a few examples for each individual case. of the carrying out ofthe invention.

V1+V2 V! i V2 Pz Storable amt. of p (Liter) (Liter) (Torr) (Torr) (Torr)gas (Torr Liters) 30 Not according to the invention 300 20 Not accordingto the invention 6 70 Not according to the invention 100 Not accordingto the invention 100 50 Not according to the invention 20 10 Notaccording to the invention 2 The following considerations are ofinterest in con- The technical improvement produced by the inventiondenection with the present invention. 40 pends on the fact that the gas(air) coming out of the lock The possible total volume and theforepressure breakchamber will be taken up for the greater part in itsown down of the diffusion or vapor jet pump are given. The forevacuumreservoir and thus the forevacuum reservoir maximum permissible pressurein the vacuum reserfor the diffusion and vapor jet pumps respectively isnot voir for the lock chamber is determined according to the loaded upand in which only a proportionally lower presamount of gas that may beexpected in the receiver sure is permitted to prevail. The suddenevacuation of which is connected to the diffusion or vapor jet pump;small containers through connecting them to other evacthis factor itselfdepends in addition on the pump conuated containers is already known andnot the object of struction and also on the kind of working fluid used,and the present invention, although, in equipment according on theproportion of the lock chamber volume to the reto the invention, theadvantage of evacuating the lock ceiver volume. It must be guaranteedthat on sudden chamber becomes important. connection to the lock chamberthe rising pressure in An especially advantageous solution of theassigned task the receiver never exceeds the value that the diffusion ofthe invention arises if the outgassing of the receiver pump will accept.This will be determined by connectitself and the objects existing Withinit are small, and the ing the second vacuum reservoir with the lockchamber greater part of the gas inflow arises from the operation for thepurpose of roughing it down and the correspondof the lock. The inventionhas advantages for other aping magnitude will be ascertained. Followingthese conplications. If for example, in the course ofelectronsiderations and with the usually available data forforemicroscopic preparations, the gas falling on photographic pressurebreakdown, the volume of the receiver as well plates and films in anelectronmicroscope consists pre as the maximum available space for bothof the foredominantly of condensible vapors such as water vapor vacuumreservoirs one arrives most easily at a 50 fold and these Vapors are ppin Cold p an so pincrease in the total storable amount of gas andcorretion trap arranged in the suction line before the foresponding to a50 fold lengthening of the undisturbed vacuum reservoir of the diffusionor vapor jet pumps, for working time with the forepump shut off.example, the oil baflle of the diffusion pump 2 below the In accordancewith the formula for the factor I}. which Valve 3 can be improved to, atthe same time act in a is easily derivable from the theory, the totalstorable known Way as a water vapor condenser, so that the foreamount ofgas in the gas of the invention is greater than Vacuum reservoir 5 ischarged only with permanent gases. for an equipment with only oneforevacuum reservoir; W Claim:

P1V1+P2V2 Yacuum apparatus havmg a receiver to which a difp i(v +Vfusion pump and forevacuum pump means are operatively 1 2 connected, alock chamber connected to said receiver where P and V are respectivelythe maximum pressure and adapted for the introduction into and removalof and the volume of the first forevacuum reservoir and objects fromsaid receiver, afirst vacuum reservoir adapted P and V signify thesimilar quantities corresponding to to be evacuated by said forevacuumpump means operathe second forevacuum reservoir. P V and P V are tivelyconnected to said diffusion pump where-by said difrespectively thecontained gas amounts at the end of the fusion pump may exhaust intosaid first vacuum reser- 5 6 voir while said forevacuum pump means istemporarily 2,291,054 7/1942 Nelson 230-101 shut off, and a secondvacuum reservoir operatively con- 2,826,353 3/1958 Auwarter 230-101nected to said forevacuum pump means and adapted to 3,117,714 1/1964Aupoix 230101 be connected directly to said lock chamber, whereby saidlock chamber may be evacuated into said second vacuum 5 FOREIGN PATENTSreservolr- 1,154,707 11/ 1957 France.

References Cited by the Examiner 1,020,151 11/1957 y- UNITED STATESPATENTS M. CARY NELSON, Primary Examiner.

2,284,710 6/1942 Zworykin 250-495 10 W. R. CLINE, Assistant Examiner.

